Whether an infant experiences dreams remains a mystery concerning the inner mental life of babies. Since infants cannot verbally report their subjective experiences, scientists study the physiology of their sleep and the limitations of their developing minds. The answer requires considering what processes must be in place for the complex, narrative experiences adults report. Understanding infant sleep patterns and early cognitive development provides a scientific framework for what their minds are doing during sleep.
How Infant Sleep Differs from Adult Sleep
The difference between a baby’s sleep and an adult’s sleep lies in the structure and duration of their sleep cycles. Adult sleep cycles last approximately 90 minutes and begin with non-rapid eye movement (NREM) sleep, the deeper, quieter stage. Newborns have much shorter sleep cycles, typically lasting only 40 to 60 minutes, which contributes to their frequent waking.
Infants cycle between two primary states: Quiet Sleep (analogous to NREM sleep) and Active Sleep (the equivalent of rapid eye movement, or REM, sleep). Active Sleep is recognizable by a baby’s physical activity, including rapid eye movements beneath closed lids, muscle twitching, and irregular breathing. This state is also characterized by a high degree of brain activity.
A newborn spends up to 50% of their total sleep time in Active Sleep, compared to the 20 to 25% adults spend in REM sleep. The duration of Active Sleep gradually decreases throughout the first year as the infant’s sleep structure matures toward the adult pattern. This physiological presence has historically led people to assume that infants are having vivid dreams, similar to adult REM dreaming.
Cognitive Development and the Capacity for Dreams
The scientific consensus suggests that the intense brain activity during infant Active Sleep is not the same as the complex, story-like dreaming of adults. Narrative dreaming requires several advanced mental capacities that infants have not yet developed. A dream involving a sequence of events and a sense of self requires developed working memory and the ability to construct narrative plots.
Infants lack the cognitive structures to form these advanced plots, suggesting their internal experiences during sleep are much simpler. The capacity to form a detailed, autobiographical sense of self, where one is the main character, typically does not emerge until a child is much older. For example, the “rouge test,” which gauges self-recognition, is usually not passed until a child is between 15 and 24 months old.
The cognitive skills needed for complex dreaming, such as generating detailed mental imagery and organizing experiences into a sequence, are developmental achievements. These abilities emerge gradually throughout childhood, with adult-like complexity in dream content and structure often not appearing until around 9 to 11 years of age. Therefore, while infants may have some basic mental content during Active Sleep, it is unlikely to be the rich, narrative experience that adults call dreaming.
The Function of Active Sleep in the Infant Brain
If Active Sleep is not narrative dreaming, its extensive duration in infancy serves a different developmental purpose. This period of high brain activity is about building and wiring the brain’s infrastructure. The brain relies on endogenous stimulation—internal activity generated by the brain itself—to drive neurological growth.
Active Sleep is crucial for synaptogenesis, the rapid formation of new neural connections that allow the brain to organize and process information. The brain practices and tests its circuits, which is necessary for consolidating basic sensory experiences gathered during waking hours, such as recognizing sounds or faces. The high-frequency electrical activity ensures the development of sensory and motor pathways.
The extensive time spent in Active Sleep reflects the brain’s rapid growth phase, requiring constant internal stimulation for maturation. The activity ensures that fundamental systems, including the visual and motor cortices, are wired correctly before the brain is fully exposed to the complexity of the external world. This developmental function is the primary utility of the high proportion of Active Sleep in the infant brain.